LOUISVILLE, Ky. - Less than five years after an explosion fueled by excess coal dust killed 29 men deep inside a West Virginia underground mine, the nation's coal mines are on pace for an all-time low in work-related deaths.

Federal mine safety officials credit changes they've made since the Upper Big Branch disaster in April 2010. They point to their more aggressive use of team inspections at problem sites and other measures, which they say have fostered more responsible behavior below ground.

"I do think we're seeing a cultural change in the mining industry that's for the better," Assistant Labor Secretary Joseph Main, who heads the U.S. Mine Safety and Health Administration, told the Associated Press.

Main took over the agency five months before the worst U.S. mining disaster in four decades, the explosion at the Massey Energy-owned Upper Big Branch mine.

Federal investigations have concluded that blast was sparked by worn and broken equipment, fueled by a deadly buildup of methane and coal dust. The former CEO of Massey, Don Blankenship, was indicted in federal court last month on charges he conspired to violate safety and health standards. Blankenship has pleaded not guilty and faces up to 31 years in prison if convicted.

Main declined to talk about the case against Blankenship because the judge has ordered the parties involved in the case to not speak publicly. The Associated Press and other media are challenging the gag order.

After Upper Big Branch, Main's agency created a list of mines with a pattern of violations and targeted them with "impact" inspections, which mobilize a team of inspectors at one site. The first list named 51 mines, and 42 were coal operations. In the years since, the agency has conducted more than 830 impact inspections, and in the latest review this year, the mines on the problem list had dwindled to 12, half of them coal mines. With a few days left in the year, there have been 15 coal mining-related deaths. The previous low was 18 in 2009.

But the improved record has coincided with a drop in coal production in Appalachia, leaving far fewer mines operating in a region where many of the worst violators have historically been found. The number of coal mines operating in the U.S. fell to 1,701 last year, from 1,944 in 2010, according to MSHA. Steady coal production in the West and a mining resurgence in the Midwest prevented an even steeper decline.